1. Field of the Invention
The present invention relates to a decoder, and in particular to a decoder for implementing an image stabilization and a digital image stabilization method using an additional information extracted from a coded bit stream.
2. Description of the Background Art
An image compression is directed to storing a large amount of image information and transmitting the same. In a mobile image communication system, a coding, decoding and transmission operation of an image is performed in real time. A motion compensation codec is capable of a large amount of image information in the mobile image communication system. When using a camcoder which adapts a motion compensation codec, a fluctuating phenomenon occurs in a user's hand, so that a degradation of image occurs due to the fluctuated hand. The digital image stabilization is directed to correct the fluctuation of the image for thereby improving a video quality of the image. Various types of digital video stabilization apparatus are introduced in the industry.
FIG. 1 is a view illustrating the construction of a digital image stabilization unit and a video codec. As shown therein, a digital image stabilization unit 10 receives a fluctuated video and outputs a stabilized video signal. A video encoder 20 receives a stabilized video signal and encodes the same. An encoded bit stream from the video encoder 20 is inputted into a video decoder 30 and is decoded thereby. Therefore, the video decoder 30 outputs a decoded video signal.
FIG. 2 is a detail block diagram of the digital image stabilization unit 10 of FIG. 1. As shown therein, a digital image stabilization unit 10 includes an image memory 10, an image enlarging unit 16 and a motion vector detector 12. The motion vector detector 12 detects a motion vector from the inputted fluctuated image. The apparatus of FIG. 2 includes a global motion vector detector 13 for detecting a global motion vector with respect to the detected motion vector, a motion vector integration unit 14 for receiving the detected global region motion vector and integrating the same, and a stabilization image output unit 15 for outputting the stabilized image from the integrated motion vector.
The digital image stabilization apparatus of FIG. 2 is used as a preprocessor of the motion compensation codec. As shown therein, the inputted fluctuated image is concurrently inputted into the image memory 11, the motion vector detector 12 and the image enlarging unit 16. The motion vector detector 12 compares the fluctuated image of the current frame with an image of a previously stored previous image. The global motion vector detector 13 detects a global motion vector which occurs based on every frame with respect to the motion vector detected by the motion vector detector 12. The detected global motion vector is outputted to the motion vector integration unit 14. In addition, the motion vector integration unit 14 integrates the inputted global motion vector, and the stabilization image output unit 15 compensates the motion using the motion vector and outputs a stabilized image. The above-described operation will be explained in detail with reference to FIG. 3.
FIG. 3 is a view illustrating a reference point in a region and a certain sub-region for estimating a motion of each sub-region by the motion vector detector 12 of FIG. 2.
The motion vector detector 12 determines three sub-regions for judging the motion due to the fluctuated state of the user's hand in two neighboring images which are continuously inputted and sets a reference point in each sub-region. In addition. The position having a highest relational value is determined as a motion vector of a sub-region by comparing the reference points of the current frame and the reference points of the previous frame. The global motion vector detector 13 receives a motion vector of each sub-region and detects a global motion vector. At this time, the motion estimation in the image having a moving object or a lower luminance may detect an erroneous vector. Therefore, in order to detect the erroneous vector, the global motion vector detector 13 is used. In the conventional art, in order to judge an accurate motion vector, it is judged using a relational value in the position which is determined as the motion vector and a relational value in the neighboring position. In the global motion vector detector 13, a global motion vector occurs based on every frame. In order to correct the fluctuating state of the image using the global motion vector, the global motion vector in the current frame is integrated as follows based on the first frame of the image sequence. The integration of the global motion vector is performed by the motion vector integration unit 14.V{right arrow over (INT)}(n)=k V{right arrow over (INT)}(n−1)+{right arrow over (VACT)}(n)  (1)
In the equation 1, V{right arrow over (INT)}(n) and V{right arrow over (ACT)}(n) are the integration motion vector and the global motion vector of the n-th frame, and “k” represents a damping coefficient.
The stabilization image output unit 15 compensates the motion using an integrated motion vector in the enlarged image inputted from the image enlarging unit 16 for thereby obtaining a stabilized image.
The conventional digital image stabilization apparatus is directed to performing a motion estimation in the input image for correcting the fluctuating state of the image, estimating the motion of the camera based on a result of the estimation and obtaining the stabilized image.
In the digital image stabilization operation, a few number of sub-regions are determined in order to decrease the amount of the computation and the complexity of the hardware without using the entire images, and the motion is estimated with respect to the determined sub-regions. In addition, in order to decrease the amount of computation, a few number of reference points are used without using all pixel values in the sub-regions. The above-described method is capable of decreasing the amount of computation using a few number of the reference points. However, a motion estimation performance is decreased due to a lack of the data used in a matching process. Therefore, in the conventional digital image stabilization technique, since a motion estimation technique is additionally used in addition to the motion estimation in the video codec, the complexity of the system is increased.